I used a Garmin c330 (now c340 I think) for awhile. It was basic but did everything I ever needed it for. It had all of the normal features - searches, mph, time to destination, voice directions, etc. The suction cup window thing stuck extremely well and made it easy to switch between vehicles (or snap free for hand-held). You can find one for $200-250 (also at Walmart).

I have the Garmin 350. It is great, very accurate and has a bunch of features I don't use such as MP3 playback, picture playback and world wide maps. The thing I love about it is that it is rechargeable, so you don't have to take the plug with you when switching between cars. It is so accurate that you can literally walk around with it if you are in a city like San Francisco. I received it this last xmas as a gift and they bought it from Amazon.com for $350, but prices might have dropped.

we have a TomTom Go portable unit, paid $150 for it during Christmas season. Great unit, no complaints. It's got a small screen, but other than that, it blows away the factory nav in our '02 beemer as well as the factory nav in our '07 Denali...for $150!